1. Technical Field
The present invention relates to the field of medical electronics. In particular, it concerns electronic devices for acquisition and presentation of diagnostic data. The invention comprises devices and procedures for acquisition and analysis of electrocardiographic (ECG) data and the three-dimensional visualization of ECG data that enables more precise diagnostic interpretation of the ECG data. According to the International Patent Classification (IPC), the invention is categorized within the A61B 5/00 class, which defines methods or devices for measurement or recording in diagnostic purposes. More precisely, the invention is categorized within the A61B 5/04 class, which defines instruments for measuring or recording bioelectric charges of a body or an organ, such as electrocardiographs.
2. Technical Problem
Although the ECG is a universally accepted diagnostic method in cardiology that dates from the beginning of the 20th century, the major problem of modern electrocardiography is the lack of cardiologists experienced in interpreting ECG recordings (Fisch, C., Centennial of the string galvanometer and the electrocardiogram, J. Am. Coll. Cardiol., 2000 Nov. 15; 36(6) 1737-45). Frequent mistakes are made in interpreting ECGs, because the most common approach for interpretation of ECGs is based on memorization of waveforms, rather than using vector concepts and basic principles of electrocardiography (Hurst, J. W., Methods used to interpret the 12-lead electrocardiogram: Pattern memorization versus the use of vector concepts, Clin. Cardiol. 2000 January; 23(1):4-13). One embodiment of this invention simplifies the vector interpretation concept, and provides a visual three-dimensional presentation of a patient's ECG signal with a three-dimensional model of the human heart, rather than relying on the cardiologist's individual spatial imagination skills. The present invention exploits a dipole approximation of electrical heart activity, in keeping with the basis of the conventional doctrine of ECG interpretation.
Another problem with traditional ECG recordings is that the ECG may not provide adequate indications of electrical activity of certain regions of the heart, especially the posterior region. An embodiment of this invention provides a more accurate approximation of cardiac activity, particularly for regions of the heart, such as the posterior region, that generally were less well represented using prior ECG recordings, and may also provide greater indications of cardiac events such as ischemia.
Furthermore, prior analysis of ECG recordings required a substantial amount of training and familiarity with reading of the recorded waveforms. An embodiment of this invention provides analysis tools to aid in the interpretation of cardiac electrical activity.
3. Background Art
There have been many attempts to extract additional information from the standard 12-lead ECG measurement when measuring the electric potential distribution on the surface of the patient's body for diagnostic purposes. These attempts have included new methods of measured signal interpretation, either with or without introducing new measurement points, in addition to the standard 12-lead ECG points. All of these are attempts to improve the spatial (i.e., the three-dimensional) aspect of interpretation.
These attempts have been conducted in several directions, including Vector ECG (VCG), modification of VCG, Electrocardiographic mapping, and Inverse Epicardiac Mapping.
Vector ECG
VCG is the oldest approach that includes the improvement of a spatial aspect to the ECG (Frank, E, An Accurate, Clinically Practical System For Spatial Vectorcardiography, Circulation 13: 737, May 1956). Like conventional ECG interpretation, VCG uses a dipole approximation of electrical heart activity. The dipole size and orientation are presented by a vector that continuously changes during the heartbeat cycle. Instead of presenting signal waveforms from the measurement points (waveforms), as it is the case with standard 12-lead ECGs, in VCG, the measurement points are positioned in such a way that three derived signals correspond to three orthogonal axes (X, Y, Z), and these signals are presented as projections of the vector hodograph onto three planes (frontal, sagittal, and horizontal). In this way, VCG represents a step towards spatial presentation of the signal, but the cardiologist's spatial imagination skills were still necessary to interpret the ECG signals, particularly the connection to the heart anatomy. Furthermore, a time-dependence aspect (i.e., the signal waveform) is lost with this procedure, and this aspect is very important for ECG interpretation. VCG introduces useful elements which cannot be found within the standard 12-lead ECG, however, the incomplete spatial presentation and loss of the time-dependence are major reasons why VCG, unlike ECG, has never been widely adopted, despite the fact that (in comparison to ECG) VCG can more often correctly diagnose cardiac problems, such as myocardial infarction.
Modifications of Vector ECG
There have been numerous attempts to overcome the drawbacks of the VCG method described above. These methods exploit the same signals as VCG (X, Y, Z), but their signal presentation is different than the VCG projection of the vector hodograph onto three planes:
“Polarcardiogram” uses Aitoff cartographic projections for the presentation of the three-dimensional vector hodographs (Sada, T., et al., Polarcardiographic study of inferior myocardial infarction: global projection of heart vector, J. Electrocardiol. 1982; 15(3):259-64).
“Spherocardiogram” adds information on the vector amplitude to the Aitoff projections, by drawing circles of variable radius (Niederberger, M., et al., A global display of the heart vector (spherocardiogram). Applicability of vector- and polarcardiographic infarct criteria, J. Electrocardiol. 1977; 10(4):341-6).
“3D VCG” projects the hodograph onto one plane, which is chosen as the most suitable for establishing a diagnosis (Morikawa, J., et al., Three-dimensional vectorcardiography (3-D VCG) by computer graphics in old myocardial infarction. Angiology, 1987 June; 38(6):449-56).
“Four-dimensional ECG” is similar to “3D VCG,” but differs in that every heartbeat cycle is presented as a separate loop, where the time variable is superimposed on one of the spatial variables (Morikawa, J., et al., Delineation of premature P waves on four-dimensional electrocardiography, a new display of electrical forces by computer techniques, Angiology, 1996 November; 47(11):1101-6).
“Chronotopocardiogram” displays a series of heart-activity time maps projected onto a sphere (Titomir, L. I., et al., Chronotopocardiography: a new method for presentation of orthogonal electrocardiograms and vectorcardiograms, Int J Biomed Comput 1987 May; 20(4):275-82).
None of these modifications of VCG been widely accepted in diagnostics, although they have some improvements over VCG.
Electrocardiographic Mapping
Electrocardiographic mapping is based on measuring signals from a number of measurement points on the patient's body (usually 25 to 200 points). Signals are presented as maps of equipotential lines on the patient's torso (McMechan, S. R., et al., Body surface ECG potential maps in acute myocardial infarction, J. Electrocardiol. 1995; 28 Suppl:184-90). This method provides significant information on the spatial dependence of electrocardiographic signals. The drawback of this method, however, is a prolonged measurement procedure in comparison to ECG, and a loose connection between the body potential map and heart anatomy.
Inverse Epicardiac Mapping
Inverse epicardiac mapping includes different methods with different names, but these methods have a few things in common: they all use the same signals for input data as those used in ECG mapping; and they are all based on numerically solving the so-called inverse problem of electrocardiography (A. van Oosterom, Incorporation of the Spatial Covariance in the Inverse Problem, Biomedizinisch Technik., vol. 42-E1, pp. 33-36, 1997). As a result, distributions of the electric potentials on the heart are obtained. These methods are very complicated, and are still being developed, and, so far, have not resulted in useful clinical devices.
All the methods described above only partially solve the problem of the spatial aspect of ECG interpretation, and all of them impose the introduction of new criteria, i.e., a new doctrine of interpretation, into cardiologic diagnostics.